#include<iostream>
#include<cstdio>
#include<cmath>
using namespace std;
int n,k,sum[150000],ma;
inline int read(){
	int k=0,f=1;char c=getchar();
	for(;!isdigit(c);c=getchar())if(c=='-')f=-1;
	for(;isdigit(c);c=getchar())k=k*10+c-'0';
	return k*f;
}
int main(){
	n=read();
	k=read();
	for(int i=1;i<=n;i++){
		sum[i]=sum[i-1]+read();
	}
	
	for(int i=1;i<=n-k+1;i++){
		ma=max(ma,sum[i+k]-sum[i]);
	}
	double ans=ma*1.0/k;
	printf("%d\n",int(ans*1000));
	return 0;
}
